Cu pillar bump with non-metal sidewall protection structure

ABSTRACT

A sidewall protection structure is provided for covering at least a portion of a sidewall surface of a bump structure, in which a protection structure on the sidewalls of a Cu pillar and a surface region of an under-bump-metallurgy (UBM) layer is formed of at least one non-metal material layers, for example a dielectric material layer, a polymer material layer, or combinations thereof.

RELATED APPLICATIONS

The present application is related to co-pending U.S. Ser. No. 12/730,411 filed on Mar. 24, 2010, which is expressly incorporated by reference herein in its entirety.

TECHNICAL FIELD

This disclosure relates to integrated circuit fabrication, and more particularly, to copper pillar bump structures in integrated circuit device.

BACKGROUND

Modern integrated circuits are made up of literally millions of active devices, such as transistors and capacitors. These devices are initially isolated from each other, but are later interconnected together to form functional circuits. Typical interconnect structures include lateral interconnections, such as metal lines (wirings), and vertical interconnections, such as vias and contacts. Interconnections are increasingly determining the limits of performance and the density of modern integrated circuits. On top of the interconnect structures, bond pads are formed and exposed on the surface of the respective chip. Electrical connections are made through bond pads to connect the chip to a package substrate or another die. Bond pads can be used for wire bonding or flip-chip bonding.

Flip-chip packaging utilizes bumps to establish electrical contact between a chip's I/O pads and the substrate or lead frame of the package. Structurally, a bump actually contains the bump itself and a so-called under bump metallurgy (UBM) located between the bump and an I/O pad. An UBM generally contains an adhesion layer, a barrier layer and a wetting layer, arranged in that order, on the I/O pad. The bumps themselves, based on the material used, are classified as solder bumps, gold bumps, copper pillar bumps and bumps with mixed metals. Recently, copper pillar bump technology has been proposed. Instead of using a solder bump, the electronic component is connected to a substrate by means of a copper pillar bump, which achieves finer pitch with minimum probability of bump bridging, reduces the capacitance load for the circuits, and allows the electronic component to perform at higher frequencies.

Cu pillar bump flip-chip assembly has the following advantages: (1) better thermal/electric performance, (2) higher current carrying capacity, (3) better resistance to electromigration, thus longer bump life, (4) minimizing molding voids—more consistence gaps between Cu pillar bumps. Also, a lower cost substrate is possible by using Cu-pillar controlled solder spreading, eliminating lead-free teardrop design. However, copper has a tendency to be oxidized during the manufacturing process. Oxidized copper pillars may lead to poor adhesion of an electronic component to a substrate. The poor adhesion may cause serious reliability concerns due to high leakage currents. Oxidized copper pillars may also lead to underfill cracking along the interface of the underfill and the copper pillars. The cracks may propagate to the underlying low-K dielectric layers or to the solder used to bond the copper pillars to the substrate. Also, during the wet etching process on the UBM layer, an isotropic etch profile is produced, in which the etching is at the same rate in all directions, leading to undercutting of the etched UBM material. This action results in an undesirable loss of bump width and makes the UBM size less than the Cu pillar size, which will cause high possibility of ELK (extreme low-k) Delamination (ED). The undercut will induce the stress concentration, resulting in Cu pillar sidewall delamination and bump crack.

A sidewall protection layer is therefore needed to prevent copper oxidation and the undercut issues, but the conventional method of processing the Cu pillar sidewall suffers from high process costs and interface delamination issues. Currently, an immersion tin (Sn) process is employed to provide a tin layer on the Cu pillar sidewalls, but there are still concerns regarding process costs, adhesion between Sn and underfill, and issues of solder wetting onto sidewalls, which is a challenge for fine pitch package technology in new generation chips.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1F are cross-sectional views of a portion of a semiconductor device at various stages in an integrated circuit manufacturing process in accordance with an exemplary embodiment;

FIGS. 2A-2E are cross-sectional views of a portion of a semiconductor device at various stages in an integrated circuit manufacturing process in accordance with another exemplary embodiment;

FIGS. 3A-3E are cross-sectional views of a portion of a semiconductor device at various stages in an integrated circuit manufacturing process in accordance with another exemplary embodiment; and

FIGS. 4A-4F are cross-sectional views of a portion of a semiconductor device at various stages in an integrated circuit manufacturing process in accordance with another exemplary embodiment.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

This disclosure provides embodiments of sidewall protection processes for Cu pillar bump technology, in which a protection structure on the sidewalls of the Cu pillar bump is formed of at least one of several non-metal material layers, for example a dielectric material layer, a polymer material layer or combinations thereof. As employed throughout this disclosure, the term “Cu pillar bump” refers to a bump structure comprising a conductive pillar (a post or a standoff) formed of copper or copper alloys. The Cu pillar bump may be applied directly on an electrical pad or a redistribution layer on a semiconductor chip for a flip chip assembly or other similar application.

Reference will now be made in detail to the present embodiments, examples of which are illustrated in the accompanying drawings. Wherever possible, the same reference numbers are used in the drawings and the description to refer to the same or like parts. In the drawings, the shape and thickness of one embodiment may be exaggerated for clarity and convenience. This description will be directed in particular to elements forming part of, or cooperating more directly with, an apparatus in accordance with the present disclosure. It is to be understood that elements not specifically shown or described may take various forms. Further, when a layer is referred to as being on another layer or “on” a substrate, it may be directly on the other layer or on the substrate, or intervening layers may also be present.

Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification are not necessarily all referring to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. It should be appreciated that the following figures are not drawn to scale; rather, these figures are merely intended for illustration.

FIGS. 1A˜1F are cross-sectional views of a portion of a semiconductor device at various stages in an integrated circuit manufacturing process in accordance with an exemplary embodiment.

With reference to FIG. 1A, there is shown a cross-sectional diagram of a semiconductor substrate 10 used for a semiconductor integrated circuit fabrication, and integrated circuits may be formed therein and/or thereupon. The semiconductor substrate is defined to mean any construction comprising semiconductor materials, including, but is not limited to, bulk silicon, a semiconductor wafer, a silicon-on-insulator (SOI) substrate, or a silicon germanium substrate. Other semiconductor materials including group III, group IV, and group V elements may also be used. The substrate 10 may further comprise a plurality of isolation features (not shown), such as shallow trench isolation (STI) features or local oxidation of silicon (LOCOS) features. The isolation features may define and isolate the various microelectronic elements (not shown). Examples of the various microelectronic elements that may be formed in the substrate 10 include transistors (e.g., metal oxide semiconductor field effect transistors (MOSFET), complementary metal oxide semiconductor (CMOS) transistors, bipolar junction transistors (BJT), high voltage transistors, high frequency transistors, p-channel and/or n-channel field effect transistors (PFETs/NFETs), etc.); resistors; diodes; capacitors; inductors; fuses; and other suitable elements. Various processes are performed to form the various microelectronic elements including deposition, etching, implantation, photolithography, annealing, and other suitable processes. The microelectronic elements are interconnected to form the integrated circuit device, such as a logic device, memory device (e.g., static random access memory or SRAM), radio frequency (RF) device, input/output (I/O) device, system-on-chip (SoC) device, combinations thereof, and other suitable types of devices.

The substrate 10 further includes inter-layer dielectric layers and a metallization structure overlying the integrated circuits. The inter-layer dielectric layers in the metallization structure include low-k dielectric materials, un-doped silicate glass (USG), silicon nitride, silicon oxynitride, or other commonly used materials. The dielectric constants (k value) of the low-k dielectric materials may be less than about 3.9, or less than about 2.8. Metal lines in the metallization structure may be formed of copper or copper alloys. One skilled in the art will realize the formation details of the metallization layers. A pad region (not shown) is a top metallization layer formed in a top-level inter-layer dielectric layer, which is a portion of conductive routes and has an exposed surface treated by a planarization process, such as chemical mechanical polishing (CMP), if necessary. Suitable materials for the pad region may include, but are not limited to, for example copper (Cu), aluminum (Al), AlCu, copper alloy, or other mobile conductive materials. The pad region is used in the bonding process to connect the integrated circuits in the respective chip to external features.

The substrate 10 further includes a passivation layer (not shown) formed overlying and exposing a portion of the pad region for allowing subsequent Cu pillar bump processes. The passivation layer is formed of a non-organic material selected from un-doped silicate glass (USG), silicon nitride, silicon oxynitride, silicon oxide, and combinations thereof. Alternatively, the passivation layer is formed of a polymer layer, such as an epoxy, polyimide, benzocyclobutene (BCB), polybenzoxazole (PBO), and the like, although other relatively soft, often organic, dielectric materials can also be used.

FIG. 1A depicts the formation of an under-bump-metallurgy (UBM) layer 12 including a first UBM layer 14 and a second UBM layer 16 on the substrate 10. For example, the UBM layer 12 is formed on the exposed portion of the pad region, and extends to a portion of the passivation layer. The first UBM layer 14, also referred to as a diffusion barrier layer or a glue layer, is formed of titanium, tantalum, titanium nitride, tantalum nitride, or the like by physical vapor deposition (PVD) or sputtering. The first UBM layer 14 is deposited to a thickness of between about 500 and 2000 angstrom, for example, to a thickness of about 1000 Angstrom. The second UBM layer 16 is a copper layer formed on the first UBM layer 14 by physical vapor deposition (PVD) or sputtering. The second UBM layer 16 may be formed of copper alloys that include silver, chromium, nickel, tin, gold, and combinations thereof. The second UBM layer 16 is deposited to a thickness of between about 500 and 10000 Angstrom, for example, to a thickness of about 5000 Angstrom.

Next, a mask layer 18 is provided on the UBM layer 12 and patterned with an opening 19 exposing a portion of the UBM layer 12 for defining a window of Cu pillar bump formation. The mask layer 18 may be a dry film or a photoresist film. The opening 19 is then partially or fully filled with a conductive material with solder wettability. In an embodiment, a copper (Cu) layer 20 is formed in the opening 19 to contact the underlying UBM layer 12. The Cu layer 20 is intended to include substantially a layer including pure elemental copper, copper containing unavoidable impurities, and copper alloys containing minor amounts of elements such as tantalum, indium, tin, zinc, manganese, chromium, titanium, germanium, strontium, platinum, magnesium, aluminum or zirconium. The formation methods may include sputtering, printing, electro plating, electroless plating, and commonly used chemical vapor deposition (CVD) methods. For example, electro-chemical plating (ECP) is carried out to form the Cu layer 20. In an exemplary embodiment, the thickness of the Cu layer 20 is greater than 25 μm. In another exemplary embodiment, the thickness of the Cu layer is greater than 40 μm. For example, the Cu layer is of about 40-50 μm thickness, or about 40-70 μm thickness, although the thickness may be greater or smaller.

With reference to FIG. 1B, the mask layer 18 is removed to expose the Cu layer 20 and a surface portion of the UBM layer 12. The Cu layer 20 protruding from the UBM layer 12 is hereinafter referred to as a Cu pillar 20 having a top surface 20 a and sidewall surfaces 20 b. In details, after removing the mask layer 18, the top surface 20 a the sidewall surfaces 20 b of the Cu pillar 20 are exposed, and a surface portion 16 a of the second UBM layer 16 adjacent to the sidewall surface 20 b is exposed as well. In the case the mask layer 18 is a dry film, it may be removed using an alkaline solution. If the mask layer 18 is formed of photoresist, it may be removed using acetone, n-methyl pyrrolidone (NMP), dimethyl sulfoxide (DMSO), aminoethoxy ethanol, and the like.

Then as shown in FIG. 1C, a protection layer 22 is formed on the resulting structure, for example by a blanket deposition. In detail, the protection layer 22 is deposited to cover the top surface 20 a and the sidewall surfaces 20 b of the Cu pillar 20, and the exposed portion 16 a of the second UBM layer 16. The protection layer 22 is a non-metal material layer, for example a dielectric material layer, a polymer material layer, or combinations thereof. The protection layer 22 may be a single material layer, or a multi-layered structure. The protection layer 22 is between about 500 Angstroms to about 10000 Angstroms thickness. In one embodiment, the protection layer 22 is a dielectric material layer formed of silicon nitride, silicon oxide, silicon oxynitride, silicon carbide, alternating layers of silicon oxide and silicon nitride, or combinations thereof by using any of a variety of deposition techniques, including thermal oxidation, LPCVD (low-pressure chemical vapor deposition), APCVD (atmospheric-pressure chemical vapor deposition), or PECVD (plasma-enhanced chemical vapor deposition). In one embodiment, the protection layer 22 is a polymer material layer and is formed of a polymer, such as an epoxy, polyimide, benzocyclobutene (BCB), polybenzoxazole (PBO), and the like, although other relatively soft, often organic, dielectric materials can also be used. The polymer material layer is soft, and hence has the function of reducing inherent stresses on respective portions of the substrate. In addition, the polymer layer is easily formed to a thickness of tens of microns.

Next, referring to FIG. 1D, certain regions of the protection layer 22 are etched to leave the portion along the sidewall surfaces 20 b, forming a sidewall spacer 22 a, also referred to as a sidewall protection structure 22 a. At this step, the protection layer 22 overlying the top surface 20 a of the Cu pillar 20 is removed, and the protection layer 22 overlying the exposed portion 16 a of the second UBM layer 16 is partially removed to leave the portion along a surface region 16 a″adjacent to the sidewall surface 20 b. Advances in lithography and masking techniques and dry etch processes, such as RIE (Reactive Ion Etching) and other plasma etching processes, allow production of the sidewall spacer 22 a.

Thereafter, referring to FIG. 1E, the UBM layer 12 is then etched using the created structure 22 a as the mask, exposing the underlying substrate 10. In an exemplary embodiment, the step of etching the UBM layer 12 is a dry etching or a wet etching. For example, an isotropic wet etching (often referred to as flash etching due to its short duration) using an ammonia-based acid is employed, or a dry etching process, such as standard RIE procedure is employed. Since the sidewall protection structure 22 a is formed on the surface region 16 a″ of the second UBM layer 16 prior to the UBM etching process, the width (W_(UBM)) of the patterned UBM layer 12 is greater than the width (W_(Pillar)) of the Cu pillar 20 measured in the same cross-section view. As to the patterned UBM layer 12, the first UBM layer 14 and the second UBM layer 16 are the same size.

The completed bump structure 24 includes the Cu pillar 20, the patterned UBM layer 12 underlying the Cu pillar 20, and the sidewall protection structure 22 a covering the sidewall surfaces 20 b and the surface region 16 a″. The substrate 10 is then sawed and packaged onto a package substrate, or another die, with solder balls or Cu bumps mounted on a pad on the package substrate or the other die.

FIG. 1F is a cross-sectional diagram depicting an exemplary embodiment of a flip-chip assembly. The structure shown in FIG. 1D is flipped upside down and attached to another substrate 100 at the bottom. The substrate 100 may be a package substrate, board (e.g., a printed circuit board (PCB)), or other suitable substrate. The bump structure 24 contacts the substrate 100 at various conductive attachment points, for example, a joint solder layer 102 on contact pads and/or conductive traces, forming a joint structure 104 a coupling the two substrates 10 and 100. The joint solder layer 102 may be a eutectic solder material including alloys of tin, lead, silver, copper, nickel, bismuth, or combinations thereof. An exemplary coupling process includes a flux application, chip placement, reflowing of melting solder joints, and cleaning of flux residue. The integrated circuit substrate 10, the joint structure 104 a, and the other substrate 100 may be referred to as a packaging assembly 200 a, or in the present embodiment, a flip-chip packaging assembly.

The disclosure provides a sidewall protection structure formed of a non-metal material on the Cu pillar sidewall to prevent the Cu pillar sidewall from oxidation and damages caused by the undercut issue in during the UBM etching process, and increase adhesion between the Cu pillar sidewall and a subsequently formed underfill material, and thereby the problems of peeling or delamination from the Cu pillar sidewall are solved. The non-metal sidewall protection structure can ensure the Cu pillar sidewall with a vertical profile, adjust substrate stress, and prevent solder wetting to the Cu pillar around the perimeter of the UBM layer during the reflow process. This is applicable to fine pitch bump schemes.

FIGS. 2A-2E are cross-sectional views of a portion of a semiconductor device at various stages in an integrated circuit manufacturing process in accordance with another exemplary embodiment. The explanation of the same or similar portions to the description in FIGS. 1A to 1F will be omitted.

With reference to FIG. 2A, there is shown a barrier layer 30 formed on the Cu pillar 20 and the UBM layer 12 after stripping the mask layer 18. In one embodiment, the barrier layer 30 covers the top surface 20 a and the sidewall surfaces 20 b of the Cu pillar 20, and the exposed portion 16 a of the second UBM layer 16. The barrier layer 30 acts as a diffusion barrier layer for preventing copper in the Cu pillar 20 from diffusing into bonding material, such as solder, that is used to bond the substrate 10 to external features. The barrier layer 30 may be also referred to as protection layer, an antioxidation layer or an oxide resistant layer employed for preventing the surfaces 20 a and 20 b of the Cu pillar 20 from oxidation during subsequent processes. The barrier layer 30 may be formed through depleting surfaces by selective thermal CVD method. The barrier layer 30 is a copper-containing material layer including a group III element, a group IV element, a group V element listed in the periodic table or any combination thereof. In one embodiment, the copper-containing material layer may include, but is not limited to, boron (B), germanium (Ge), silicon (Si), carbon (C), nitrogen (N), phosphorous (P) or combinations thereof. In some embodiments, the copper-containing material layer is a CuGeN layer, a CuGe layer, a CuSi layer, a CuSiN layer, a CuSiGeN layer, a CuN layer, a CuP layer, a CuC layer, a CuB layer, or combinations thereof, using a selective CVD with gases containing B, Ge, Si, C, N, P or combinations thereof (e.g., B₂H₆, CH₄, SiH₄, GeH₄, NH₃, PH₃). For an example of forming a CuGeN layer, a deoxidization treatment step (NH₃ treatment) is performed followed by a GeH₄ CVD process. The barrier layer 30 becomes a diffusion barrier layer to passivate the Cu from the solder in subsequent joint processes so that the IMC formation is controlled to become thinner and more uniform. The thickness of the barrier layer 30 is thin, because its formation is like a diffusion process. In one embodiment, the thickness of the barrier layer 30 is less than or equal to 10 nm.

With reference to FIG. 2B, a protection layer 22 is formed on the barrier layer 30, for example by a blanket deposition. The protection layer 22 is a non-metal material layer, for example a dielectric material layer, a polymer material layer or combinations thereof. The protection layer 22 may be a single material layer, or a multi-layered structure. In one embodiment, the protection layer 22 is a dielectric material layer formed of silicon nitride, silicon oxide, silicon oxynitride, silicon carbide, alternating layers of silicon oxide and silicon nitride, or combinations thereof. In one embodiment, the protection layer 22 is a polymer material layer and is formed of a polymer, such as an epoxy, polyimide, benzocyclobutene (BCB), polybenzoxazole (PBO), and the like.

Next, referring to FIG. 2C, certain regions of the protection layer 22 are etched to leave the portion along the sidewall surfaces 20 b, forming a sidewall spacer 22 a, also referred to as a sidewall protection structure 22 a. At this step, the protection layer 22 over the top surface 20 a of the Cu pillar 20 is removed, and the protection layer 22 over the exposed portion 16 a of the second UBM layer 16 is partially removed to leave the portion over a surface region 16 a″adjacent to the sidewall surface 20 b. The barrier layer 30 may remain on the top surface 20 a of the Cu pillar 20 and the portion 16 a of the second UBM layer 16 at this step.

Then, as shown in FIG. 2D, the barrier layer 30 and UBM layer 12 are etched using the created structure 22 a as the mask, exposing the underlying substrate 10. The barrier layer 30 may be removed from the top surface 20 a and a part of the portion 16 a at this step. The completed bump structure 32 includes the Cu pillar 20, the UBM layer 12 underlying the Cu pillar 20, the sidewall protection structure 22 a over the sidewall surfaces 20 b and the surface region 16 a″, and the barrier layer 30 sandwiched among the sidewall protection structure 22 a, the sidewall surfaces 20 b and the surface region 16 a″.

Referring to FIG. 2E, the substrate 10 is flipped upside down and attached to another substrate 100 at the bottom. The bump structure 32 contacts the substrate 100 at various conductive attachment points, for example, a joint solder layer 102 on contact pads and/or conductive traces, forming a joint structure 104 b coupling the two substrates 10 and 100. The joint solder layer 102 may be a eutectic solder material including alloys of tin, lead, silver, copper, nickel, bismuth, or combinations thereof. The integrated circuit substrate 10, the joint structure 104 b, and the other substrate 100 may be referred to as a packaging assembly 200 b, or in the present embodiment, a flip-chip packaging assembly.

The disclosure provides a barrier layer containing copper and germanium formed between a sidewall protection structure and the Cu pillar sidewall, which can further prevent the Cu pillar sidewall from oxidation and increase adhesion between the Cu pillar sidewall and a subsequently formed underfill material. This prevents solder wetting to the Cu pillar around the perimeter of the UBM layer during the reflow process. The barrier layer does not compromise resistance (Rs) much.

FIGS. 3A-3E are cross-sectional views of a portion of a semiconductor device at various stages in an integrated circuit manufacturing process in accordance with another exemplary embodiment. The explanation of the same or similar portions to the description in FIGS. 1A to 1F will be omitted.

With reference to FIG. 3A, there is shown a cap layer 40 formed on the top surface 20 a of the Cu layer 20 before the formation of the Cu layer 20 in the opening 19 of the mask layer 18. The cap layer 40 could act as a barrier layer to prevent copper in the Cu pillar from diffusing into bonding material, such as solder alloy, that is used to bond the substrate 10 to external features. The prevention of copper diffusion increases the reliability and bonding strength of the package. The cap layer 40 may include nickel (Ni), tin, tin-lead (SnPb), gold (Au), silver, palladium (Pd), indium (In), nickel-palladium-gold (NiPdAu), nickel-gold (NiAu), other similar materials, or alloys deposited by plating methods. The cap layer 40 has a thickness about 1-10 μm. In some embodiments, the cap layer 40 is a multi-layer structure including a first metal film 42 and a second metal film 44. The first metal film 42 may include Ni, Au, Pd, Ni-base alloy, Au-base alloy, or Pd-base alloy. The second metal film 44 may include Ni, Au, Pd, Ni-base alloy, Au-base alloy, or Pd-base alloy. In one embodiment, the first metal film 42 is a Ni film, and the second metal film 44 is an Au film. Each of the first metal film 42 and the second metal film 44 has a thickness about 1-5 μm.

Next, as shown in FIG. 3B, the mask layer 18 is removed to expose the sidewall surfaces 20 b and the portion 16 a, and the top surface 40 a. The sidewall surfaces 40 b of the cap layer 40 are also exposed at this step. Then, as depicted in FIG. 3C, a protection layer 22 is formed on the resulting structure, to cover the cap layer 40, the sidewall surfaces 20 b of the Cu pillar 20, and the exposed portion 16 a of the second UBM layer 16. After performing lithography and masking techniques and dry etch processes, a sidewall protection structure 22 a is created. The top surface 40 a of the cap layer 40 is therefore exposed. The UBM layer 12 is then etched using the created structure 22 a as the mask, exposing the underlying substrate 10, as depicted in FIG. 3D.

The completed bump structure 46 includes the Cu pillar 20, the cap layer 40 on the top surface 20 a of the Cu pillar 20, the patterned UBM layer 12 underlying the Cu pillar 20, and the sidewall protection structure 22 a covering the sidewall surfaces 40 b and 20 b and the surface region 16 a″. The substrate 10 is then sawed and packaged onto a package substrate, or another die, with solder balls or Cu bumps mounted on a pad on the package substrate or the other die.

Referring to FIG. 3E, the substrate 10 is flipped upside down and attached to another substrate 100 at the bottom. The bump structure 46 contacts the substrate 100 at various conductive attachment points, for example, a joint solder layer 102 on contact pads and/or conductive traces, forming a joint structure 104 c coupling the two substrates 10 and 100. The integrated circuit substrate 10, the joint structure 104, and the other substrate 100 may be referred to as a packaging assembly 200 c, or in the present embodiment, a flip-chip packaging assembly.

FIGS. 4A-4F are cross-sectional views of a portion of a semiconductor device at various stages in an integrated circuit manufacturing process in accordance with another exemplary embodiment. The explanation of the same or similar portions to the description in FIGS. 3A to 3E will be omitted.

With reference to FIG. 4A, there is shown a solder layer 50 formed on the top surface 40 a of the cap layer 40 after the formation of the cap layer 40 on the Cu layer 20. The solder layer 50 may be made of Sn, SnAg, Sn—Pb, SnAgCu (with Cu weight percentage less than 0.3%), SnAgZn, SnZn, SnBi—In, Sn—In, Sn—Au, SnPb, SnCu, SnZnIn, or SnAgSb, etc., formed by plating processes. In one embodiment, the solder layer 50 is a lead-free solder layer. For a lead-free solder system, the solder layer is SnAg with Ag content being controlled lower than 3.0 weight percent (wt %). For example, the lead-free solder layer is SnAg with Ag content being controlled at about 2.5 weight percent (wt %).

Next, as shown in FIG. 4B, the mask layer 18 is stripped to expose the sidewall surfaces 40 b and 20 b and the portion 16 a, and the top surface 50 a and the sidewall surfaces 50 b of the solder layer 50 are also exposed at this step. Thereafter, as depicted in FIG. 4C, a protection layer 22 is formed on the resulting structure, to cover the solder layer 50, the cap layer 40, the sidewall surfaces 20 b of the Cu pillar 20 and the exposed portion 16 a of the second UBM layer 16. After performing lithography and masking techniques and dry etch processes, a sidewall protection structure 22 a is created as depicted in FIG. 4D. The top surface 50 a of the solder layer 50 is therefore exposed. The UBM layer 12 is then etched using the created structure 22 a as the mask, exposing the underlying substrate 10.

With reference to FIG. 4E, a reflowing process is performed on the solder layer 50 to form a reflowed solder layer 50″ on the cap layer 40. This completes a bump structure 52 that includes the Cu pillar 20, the cap layer 40 on the Cu pillar 20, the reflowed solder layer 50″ on the cap layer 40, the patterned UBM layer 12 underlying the Cu pillar 20, and the sidewall protection structure 22 a covering the sidewall surfaces 40 b and 20 b and the surface region 16 a″. The substrate 10 is then sawed and packaged onto a package substrate, or another die, with solder balls or Cu bumps mounted on a pad on the package substrate or the other die.

Referring to FIG. 4F, the substrate 10 is flipped upside down and attached to another substrate 100 at the bottom. The bump structure 52 contacts the substrate 100 at various conductive attachment points, for example, a joint solder layer 102 on contact pads and/or conductive traces, forming a joint structure 104 d coupling the two substrates 10 and 100. The integrated circuit substrate 10, the joint structure 104 d, and the other substrate 100 may be referred to as a packaging assembly 200 d, or in the present embodiment, a flip-chip packaging assembly.

In the preceding detailed description, the disclosure is described with reference to specific exemplary embodiments thereof. It will, however, be evident that various modifications, structures, processes, and changes may be made thereto without departing from the broader spirit and scope of the disclosure. The specification and drawings are, accordingly, to be regarded as illustrative and not restrictive. It is understood that the disclosure is capable of using various other combinations and environments and is capable of changes or modifications within the scope of the inventive concepts as expressed herein. 

What is claimed is:
 1. An integrated circuit device, comprising: a semiconductor substrate; a conductive pillar formed over the semiconductor substrate, and having a sidewall surface and a top surface; a under-bump-metallurgy (UBM) layer formed between the semiconductor substrate and the conductive pillar, and having a surface region adjacent to and extending from the sidewall surface of the conductive pillar; and a protection structure formed on the sidewall surface of the conductive pillar and the surface region of the UBM layer; wherein the protection structure is formed of a non-metal material, and the conductive pillar is formed of a copper-containing layer.
 2. The integrated circuit device of claim 1, wherein the protection structure comprises a silicon nitride layer.
 3. The integrated circuit device of claim 1, wherein the protection structure comprises a polyimide layer.
 4. The integrated circuit device of claim 1, wherein the protection structure comprises at least one of a dielectric layer, a polymer layer, or combinations thereof.
 5. The integrated circuit device of claim 1, wherein the UBM layer comprises a first UBM layer formed on the semiconductor substrate, and a second UBM layer formed on the first UBM layer, and wherein the first UBM layer and the second UBM layer have the same size.
 6. The integrated circuit device of claim 1, further comprising a barrier layer formed between the UBM layer and the protection structure, wherein the barrier layer is a copper-containing material layer comprising Ge, Si, N, or combinations thereof.
 7. The integrated circuit device of claim 1, further comprising a barrier layer formed between the conductive pillar and the protection structure, wherein the barrier layer is a copper-containing material layer comprising Ge, Si, N, or combinations thereof.
 8. The integrated circuit device of claim 1, further comprising a cap layer on the top surface of the conductive pillar.
 9. The integrated circuit device of claim 8, wherein the cap layer comprises a Ni layer on the top surface of the conductive pillar, and an Au layer on the Ni layer.
 10. The integrated circuit device of claim 8, further comprising a solder layer formed on the cap layer.
 11. The integrated circuit device of claim 10, wherein the protection structure extends to cover at least a portion of the sidewall surface of the cap layer and the sidewall surface of the solder layer.
 12. The integrated circuit device of claim 8, wherein the protection structure extends to cover at least a portion of the sidewall surface of the cap layer.
 13. A packaging assembly, comprising: a first substrate; a bump structure formed on the first substrate, wherein the bump structure comprises an under-bump-metallurgy (UBM) layer formed on the first substrate, and a copper pillar formed on the UBM layer, wherein the UBM layer has a surface region adjacent to and extending from a sidewall surface of the copper pillar; a non-metal protection structure covering the sidewall surface of the copper pillar and the surface region of the UBM layer; a second substrate; and a joint solder layer formed between the second substrate and the bump structure.
 14. The packaging assembly of claim 13, wherein the non-metal protection structure comprises a silicon nitride layer.
 15. The packaging assembly of claim 13, wherein the non-metal protection structure comprises a polyimide layer.
 16. The packaging assembly of claim 13, wherein the non-metal protection structure comprises at least one of a dielectric layer, a polymer layer, or combinations thereof.
 17. The packaging assembly of claim 13, further comprising a barrier layer formed among the UBM layer, the non-metal protection structure and the copper pillar, wherein the barrier layer is a copper-containing material layer comprising Ge, Si, N, or combinations thereof.
 18. The packaging assembly of claim 13, further comprising a cap layer on a top surface of the copper pillar.
 19. The packaging assembly of claim 18, wherein the cap layer comprises a Ni layer on the top surface of the copper pillar, and an Au layer on the Ni layer.
 20. The packaging assembly of claim 18, further comprising a solder layer formed on the cap layer. 